1. Technical Field
This invention relates to a subsea sonar unit comprising an acoustic transducer embedded in a protective oil where the acoustic transducer defines an acoustic propagation path for acoustic signals to or from the transducer, wherein the oil is contained in a housing, and the housing having an acoustically transparent surface with a known shape. More specifically includes a corrective lens for underwater transducers with protective oil dome to improve their performances at extreme condition and different types of oils.
2. History of Related Art
Various acoustic lenses are well known for use in medical ultrasonic probes in order to focus and control the beam angle and focal point mostly for high frequency. Different types of acoustic lenses for use in sonars are known, such as described in U.S. Pat. No. 3,990,035, U.S. Pat. No. 4,168,482 and U.S. Pat. No. 6,377,514. However, no satisfactory lenses have been proposed for use in sonar at extreme condition and lower frequencies.
Most of Offshore and Fisheries scanning sonar have a protective oil filled dome on the transducer. The transmitted wave from transducer goes through oil and passes the concave interface of oil-dome wall-water. The selected materials for dome and selected oil, normally has sound speed close to the water at room temperature and atmosphere pressure, therefore the ultrasonic beam does not deflect at interface of oil-water. But at higher-lower temperatures and pressures the sound speed changes differently for oil and water that cause the deflection of beam and consequently deteriorate the sonar performance.